1. Field of the Invention
The present invention relates generally to a yoke type magnetic transducer head utilizing the magnetoresistance effect and, more particularly, is directed to a structure of a yoke type magnetic transducer head utilizing the magnetoresistance effect for applying a bias to a magnetoresistance effect sensing portion thereof.
2. Description of the Prior Art
A structure of a prior art yoke type magnetic transducer head utilizing the magnetoresistance effect (hereinafter simply referred to as a yoke type MR head) will be described with reference to FIG. 1.
Referring to FIG. 1, on a magnetic substrate 1, there is formed a bias conductor 3 made of a band-shaped conductive film. When the magnetic substrate 1 has conductivity, this bias conductor 3 is formed on the magnetic substrate 1 through an insulating layer 2 made of SiO.sub.2 and the like. This bias conductor 3 is formed on the magnetic substrate 1 through an insulating layer 21 made of SiO.sub.2 and the like. This bias conductor 3 is adapted to apply a bias magnetic field to a magnetoresistance effect sensing portion (hereinafter simply referred to as an MR portion) 5 which will be described later. The magnetic substrate 1 is made of a soft magnetic ferrite such as an Ni-Zn ferrite or an Mn-Zn ferrite, while the bias conductor 3 is made of, for example, Cu.
On the bias conductor 3, there is formed through an insulating layer 4 made of SiO.sub.2 or the like a magnetic thin film having the magnetoresistance effect which forms the MR sensing portion 5. The MR thin film is made of Ni-Fe alloys, Ni-Co alloys and the like and the width thereof is selected to be W.sub.MR. An insulating layer 6 is formed on the MR sensing portion 5.
Magnetic layers 7a and 7b are respectively formed to be extended along the direction to traverse the bias conductor 3 and the MR sensing portion 5 with their one ends superposed on both ends of the MR sensing portion 5. The magnetic layers 7a and 7b are made of soft magnetic material such as M.sub.O permalloy and the like and constitute a magnetic yoke 8. To the upper surface of the MR head portion thus constructed, there is bonded a protecting substrate 10 made of glass and the like through a protecting layer 9 made of non-magnetic insulating material such as SiO.sub.2 and the like.
A non-magnetic gap spacer layer (a part of the insulating layer 2) 11 is interposed between one magnetic layer 7a and the front end portion of the magnetic substrate 1 to form a front magnetic operation gap g. The front surfaces of the magnetic substrate 1, the gap spacer layer 11, the magnetic layer 7a, the protecting layer 9 and the protecting substrate 10 are polished so as to face the magnetic gap g to the outside, thus forming a magnetic recording medium contact surface 12.
A cut-away portion 13 having a width W is formed between the opposing end surfaces of the magnetic layers 7a and 7b. The rear end and the front end of both the magnetic layers 7a and 7b are electrically insulated from both sides of the MR sensing portion 5 due to the existence of the insulating layer 6 but are magnetically coupled with each other. The portions of the magnetic layers 7a and 7b separated by the cut-out portion 13 of the magnetic yoke 8 are coupled to each other via the MR sensing portion 5 thereby forming a magnetic circuit which forms a closed magnetic path from the magnetic substrate 1 through the operation gap g, the magnetic layer 7(a), the MR sensing portion 5 and the magnetic layer 7(b) to the magnetic substrate 1.
In such a yoke type MR magnetic transducer head, by supplying a bias current to the bias conductor 3, it is possible to apply a predetermined bias magnetic field to the MR sensing portion 5 by which a linear reproduced output is derived.
Upon the playback mode of the yoke type MR magnetic transducer head thus constructed, it is possible to apply a bias magnetic field to the MR sensing portion 5 by flowing a bias current (D.C. current) to the bias conductor 3. Further, a sense current is supplied to the MR sensing portion 5. A magnetic flux generated by these currents passes through not only the MR sensing portion 5 but also the magnetic yoke 8,that is, the magnetic layers 7a and 7b as shown by a one-dot chain line MF.sub.1 in FIG. 1. As a result, the permeability of the magnetic yoke 8 is lowered and the sensitivity (maximum sensitivity) of the head is lowered and scattered. Also a Barkhausen noise may readily occur, and is not desirable.
Similar problems will take part more or less in a yoke type magnetic transducer head utilizing the magnetoresistance effect but which has no bias conductor. The reason for this is that when a sense current is flowed to the MRT sensing portion 5, magnetic flux is generated therearound. Then, the magnetic bias is applied to the MR sensing portion itself by the magnetic flux. In this case, part of this magnetic flux is passed through the magnetic yoke.